. 2014 Jun 19;11(6):6400–6416. doi: 10.3390/ijerph110606400

Table 2.

Summary of gravimetric equivalency conversion for the three humidity adjusted results (with and without a 60% RH threshold) utilizing a linear, linear with log transformed variables, linear with log transformed and spline variable, and linear with log transformed and quadratic variable Equations.

Equation Type	Coefficient and RMSE Values	With Threshold			Without Threshold
Equation Type	Coefficient and RMSE Values	Equation 1a	Equation 1b	Equation 2a	Equation 1a	Equation 1b	Equation 2a
Linear eqn. (Equation (3))	a	0	0	0	0	0	0
	b	0.848	0.845	0.831	0.892	0.757	0.696
	RMSE ^†	3927	4002	4005	3956	3982	3955
Linear eqn. w/log transformed variables (Equation 4)	a	2.726	2.750	2.753	2.723	2.510	2.395
	b	0.711	0.707	0.706	0.715	0.724	0.730
	RMSE ^†	2889	2977	2969	2932	3001	2990
Linear eqn. w/log transformed and spline variables (Equation 5)	a	0.859 *	0.872 *	0.822 *	0.565 *	0.921 *	0.868 *
	b	0.949	0.948	0.953	0.995	0.921	0.917
	c	−4.051	−0.411	−0.416	−0.430	−0.471	−0.502
	d	8.4	8.4	8.4	8.2	8.9	9.1
	RMSE ^†	2703	2768	2773	2742	2650	2620
Linear eqn. w/log transformed and quadratic variables (Equation 6)	a	−4.867 *	−4.945	−4.951	−4.994 *	−6.049	−6.607
	b	2.502	2.527	2.522	2.544	2.722	2.809
	c	−0.105	−0.106	−0.106	−0.107	−0.115	−0.119
	RMSE ^†	2682	2750	2759	2715	2652	2619

Notes: * Not significantly different from 0 (p > 0.05); ^† RMSE is μg/m³.